Process for recovering acetylene



April 1.0, 1956 .1. A. FlNNl-:RAN TAL 2,741,332

PROCESS FOR RECOVERING ACETYLENE Filed Feb. 29, 1952 i.. .Pfl

2,741,332 p Y PRoCEss son nac venuto acnrvrnnn James A. Finneran, Westbury, N. Y., and Herman N. Woebche, Emerson, N. J., assignors to Hydrocarbon Research, Inc., New Yori-t, N. Y., a corporation or New Jersey Application Fsama/ ze, rasa, sans; m1745188 12 cierras.' (ci. tas- 115) This invention relates to the isolation and Vpurication of acetylene present in low concentration in gaseous streams which are produced by acetylene manufacturing processes employing a hydrocarbon as a charge material. The process of the invention is particularly applicable to the recovery of acetylene in a highly purified state from the gaseous product mixture obtained by short Contact time-incomplete combustion of a hydrocarbon.

'l`he classic method of preparing acetylene which invoives the reaction oi water with calcium carbide. has recently been challenged by newer processes for producing acetylene which are based on natural gas as acharge material. The activity in the acetylene eld hasbeen enormously stimulated by Reppes developments in the eld of acetylene chemistry and ny the rapid development 2,741,332 lamented Apr. i0, i956 ICC tra

derived'from the secondary absorption step is then contacted with a selective solvent for acetylene, for example, trisdimethylamido phosphate (TDMAP) or dimethyl formamide (DMF). The selective solvent removes substantially all ofthe acetylene from the gas stream and also removes a portion of the carbon dioxide present in the product gas. The carbon dioxide is removed from the rich solvent by prestripping with acetylene to yield an overhead gas comprising carbon dioxide and acetylene which overhead gas is compressed and recycled to the primary absorption tower. Tne acetylene is nally stripped from the rich solvent by increasing the temperature or by decreasing the pressure.

It has been discovered that a one-step absorption of l5 tars, aromatic hydrocarbons and higher acetylenes as practiced prior to this invention is extremely hazardous and causes operating diiculties in the nature of sludges, deposits and plugs formed in therecovery unit, particularly in the exchangers. Apparently, highly explosive 2O compounds are formed by reactions of aromatics and higher acetylenes such as vinyl acetylene and diacetylene when allthe by-products are removed from the acetylenecontaining product stream in a single absorption stage. The success of the process ofy this invention appears Vto stem from conducting the rirst absorption under controlled conditions so that 90% or more of the tars and aromatic hydrocarbons in the gaseous stream are removed therefrom with minimum absorption of vinyl acetylene and 'diacctylene which are primarily removed in the secondiabsorption;V t is believed fortunate and a contributing vfaci'nclude the Schoch process which involves subjecting nat- Aural gas to electric discharge, the so-called SachseV processY which involves partial oxidation of methane .with oxygen at elevatedtemperature and short contacttime, and-the Willi Y process which produces, acetylene by thermally cracking a hydrocarbonin-a regenerative urnaca. All or" these processes yield a gaseous product stream in which the acetylene is a minor constituent, usually less than 10% by volume of the product stream. lt is. apparent that one of the most important requirements for raising these lnew acetylene processes to commercial status is the development of an etlicient recovery and purification system.

The present invention provides an answer to the need for an e'icient, foolproof system for recovering acetylene in a high degree of purity from the dilute streams produced by decomposition of a hydrocarbon. The process of this invention generally results in recovery of acetylene from the gaseous product stream in better than 98% by volume purity. in addition, the present invention minimizes the hazards otacetylene recovery and is the safest and most ecient means yet devised for the separation of acetylene from dilute gaseous streams.V

ln. accordance with the process of this invention, acety- 55 absorber and the remaining higher acetylenes, particularly vinyl acetylene and diacetylene in the second absorber, and a third absorption step for acetylene recovery from the residual gas. in the primary absorption tower the product gas stream is contacted at a temperatuterof 3G to 100 F. and at a pressure of approximately atmospheric to 150 p. s. i. g. with a small proportion ofa highly para'inic gas oil. The gas stream, after ow throughthe first absorber, is contacted in a secondary absorption tower with a larger proportion ot paraninic gas oil at a pressure of approximately' atmospheric to 150 p. s. i. g. and at-a similar temperature of 30 to 100 F. The gas stream Twill, also be removed, rl`he operating conditions required Ytor to the success` of this process thatvwhen the first absorber is controlled to remove 90% or moreof the aro-v `,matic V hydrocarbons in the gas. stream, more than 90% of the phenyl acetylene and triacetylene in the gas stream to effect such stage-wise; removal of by-products are important features of this invention. I,

VTo achieve the desired stagewise removal ofjby-produc t s`, 'the gaseous stream is contacted with highly paraiinic 40 gas oil, desrably having aboiling point range of 400` to 500 F., in the first absorber in the proportion of 1 gallon perfil): to cubicv feet of gas .passing'therethrough (the lgas volume being measured at the conditions existing in the absorber), preferably l gallon per 40 to 50 cubic feet. The rich absorber oil is stripped of absorbed by products either by heating or by reducing the pressure on the oil; a stripping gas, such as nitrogen or a mixture of hydrogen and carbon monoxide, is usually employed to facilitate stripping.

After passing through the iirst absorber, the gaseous stream contacts highly paraffmic gas oil in the second absorber in the proportion of 1 gallon per 3 to 6 cubic feet of gas passing therethrough (the gas volume being measured at. the conditionsexisting in the absorber), preferably 1 gallon per 4 to 5 cubic feet.

Since approximately 5 to 7% of the acetylene is removed from the productrs'tream in the secondaryabsorber, it is necessary to prestrip the rich oil from the secondary absorber. Accordingly, a portion of the residue gas comprising mainly carbonmonoxide and hydrogen is contacted"with the rich oil at atmosphericpressure and at a temperature or 35 to 1'30" F. Substantially all of the acetylene absorbed in the secondary absorber is removed from the rich absorber'oil by this treatment and is recycled to the primary absorber. After acetylene removal by prestripping, higher Vacetylenes, principally vinyl acetylene and diacetylene, are removed from the rich oil either -by bubbling a stripping gas such as residue gas or nitrogen 'therethrough at atmospheric pressure and a temperature of approximately 106 F. or by treatment with the same gases at. a lower temperature and at reduced pressure.

After the primary and secondary absorption steps, the

product gas is substantially tree of benzene, higher arotemperature in the range of about 30 to 100 F. and at a Ypressure-from about atmospheric to 150 p. s. i. g. Aproximately 1 gallon of TDMAP is made to ow through the third absorber for every 5 to 10 cubic feet of gaspassing therethrough (the gas volume being measured kat the conditions existing in the absorber). The kflowfrate for DMF is approximately 1 gallon for every 3l to 7 `cubic feet of gas.

Approximately 99% of the acetylene presentin the product gas is removed in the third absorber. Approximately A7%V of the carbon dioxide present in theV product gas is also absorbed. Accordingly, prior to recovery of acetylene from the rich solvent, the rich solvent is pre- -vstripped with acetylene to remove carbon dioxide. The overhead gas from the stripping operationlis recycled to the first absorber-for reprocessing in accordance-with this invention. The prestripping of Vtherich vsolvent may Vbe effected Vat a temperature of the order ofY 165 Rand at Y'atmospherictpressure. Recovery. of acetylene from @the rich solvent after carbon dioxide prestripping, effectled by further increasing the temperature and .decreasing Ithepressure. Y v recirculated to the third absorption tower.

The selective solvent is then cooled and The acetylene recovered by the process of theiinven- 'tion contains less than 0.4 mol percent of methylacetyv lene. While acetylene of this purity is often acceptable, Vit is sometimes desirable to produce acetylene containing less thanV 0.15 mol percentof'methyl acetyleneln such nevent, the recovered'acetylene may be subjected to a.

purication step involving contact with light, naphtha. The acetylene isscrubbed with light naphthaat atmos- Apherie pressure and at a temperature of about'30 to 60 F. *whereby the methyl acetylene is preferentially Yremoved from the' product acetylene. Since contact with light naphtha also absorbs a substantial percentage of acetylene, vit is advisable tosubject the. rich naphtha to a prestripping operation which merelyinvolves reboiling therich naphtha at a temperature of about 200 F. and atmospheric 'pressure in order to drive off the acetylene. Thereafter,

the rich naphtha is stripped of methylacetylene.

The process of the invention will be illustrated by the isolation and recovery of high'purity acetylene from the product stream obtained by partial combustion of natural gas with oxygen at a temperature between about 2500 `and 3000 F., desirably at about 2800 F., at atmospheric pressure, and at a contact time of about 0.001 to 0.1 second, preferably less than about 0.01 second. The typical product stream produced by the partial combustion` of methane at the aforesaid conditions contains on a volume `basis approximately 8% acetylene, 0.2% benzene and higher boiling aromatics, 0.1% phenyl acetylene and triacetylene, 0.4%'diacetylene, 0.1% vinyl acetylene, 0.2%

'methyl acetylene-4% carbon dioxide and the remainder comprising principally hydrogen and carbon monoxide with minor amounts of nitrogen and methane; the afore- Y said remainder comprises approximately 75 to 85% hydrogen and carbon monoxide in approximately a 2`11mol ratio. Y

VReferring to the accompanying drawing which `isoneA diagrammatic ilowsheet of the Vprocess of this invention,

thegaseous product'stream obtained by the partial combustion of natural gas with high-purity oxygen is passed through a water scrubber 1A wherein the gaseous stream is scrubbed with water to remove entrained carbon particles, tar mist and water-soluble compounds. While the water-scrubbing step is ,of value in connection with any TheV amnesia gaseous stream to be processed in accordance with this invention because such stream usually carries in suspension carbon particles, tar mist and dust particles' which can be washed from the gaseous stream, water-scrubbing is particularly important for any gaseous stream producedV by the partial oxidation of ahydrocarbon as is the'case so t' iu the illustrative example of the appended owsheet.

quantities of hydrocyanic acid, nitrogen oxides and koxygenated hydrocarbons that are formed during the highotherwise tend to react or catalyze reactions and/ or causeY foaming in the absorber liquid.

The washed gas flows through pipe 1 into compressor 2, which preferably contains two stages and is provided with means for pre, inter, andy after-cooling. The gaseous stream leaves the compressor at approximately p. s. i. g. through pipe 3 and is introduced into primary absorber 4, maintained under refrigeration at a temperature of about F., wherein the stream is contacted with ahighly paranc gas oil in the proportion of i gallon per 45 cubic feet of gas. The gas oil is introduced into the absorber through pipe 5. At the prescribed conditions, at least 95% of the benzene and higheraromatics are removed from the gaseous stream along with substantially all phenyl acetylene and triacetylene but with no substantial absorption of other acetylenes.

f The rich absorber oil is withdrawn the absorbed materials are removed yfrom the absorber'oil 1 by stripping with nitrogen at a temperature of about 80 F. YThe nitrogen is introduced, into stripping tower 9 through pipe 10. Nitrogen and stripped materialsare .removed from the upperportion of tower 9 through pipe with one gallon of highly paratlinic gasoil per 4 cubic `feet of gas. The gas oil is introduced into the upper part of absorber tower 16 through pipe 17. Contact ofthe gaseous stream with gas oil under the prescribed conditions etlects removal of at least of the higher acetylenes, particularly vinyl acetylene and diacetylene, and absorption of about 6% of the total acetylene present in the stream.

troduced through pipe 22. The acetylene-containing gas Y is removed from prestripper 20 through pipe 21 andV recycled to compressor 2 and thence to primary absorber 4. The rich absorberV oil from which acetylene has4 been Vstripped is withdrawn from yprestripper 20 through pipe 25 and introduced into stripper 26 wherein absorbed higher acetylenes are removed from the absorber oil by contact at atmospheric pressure and a temperature of F.

y with inert residual gas introduced through pipe 43'. VVThe In such instance, the gaseous strearnfappears to havejsm'all from absorber4 Y through pipe V8, and is introduced intogstripper 9 wherein ,s duced into absorber 35 wherein it is contacted with TDMAP at a pressureof p. s. i. g. and a temperature of about 40 F. The heat of solution causes the temperature to rise considerably in tower 3,5, but precautions are taken so that the temperature does not rise above approximately 80 F. TDMAP is introduced into-the upper portion of tower through pipe 36 in the proportion of one gallon per 8 cubic feet of gas. More than 99% by voli tha is withdrawn from the bottom of stripper '65 through pipe 67 and recycled to'absorber 55. y

The acetylene recovered from the naphtha purification step is of extremely high purity as indicated byv its comurne of the acetylene in the gaseous stream is absorbed therefrom by this treatment so that there is obtained a residual gas containing less than 0.1% by volume of acetylene. This residual gas comprises mainly carbon monoxide and hydrogen with minor quantities of carbon dioxide and methane and thus is a valuable fuel gas or reactant gasfor the synthesis of hydrocarbons, ammonia and other chemicals. A portion of the residual gas is removed from tower 35 through pipe 38 for such utilization, while the remainder is passed through lines 39 and 43 to serve as theA stripping gas in prestripper 20 and stripper 26, respectively.

Since TDMAP also absorbs some carbon dioxide from the gaseous stream, it is necessary to subject the rich solvent to carbon dioxide stripping prior to recovery of acetylene therefrom. To this end, the rich solvent is withdrawn from tower 35 through pipe 40 and introduced into stripping zone 41 wherein it is contacted with product acetylene at 1 p. s. i. g. pressure and a temperature of 165 F. The carbon dioxide stripping requires approximately 3 cubic feet of acetylene per gallon of solvent; the acetylene is introduced into stripping tower 41 through pipe 42. The mixture of stripped carbon dioxide and acetylene stripping gas is removed overhead from tower 41 through pipe 44 and recycled therethrough to compressor 2.

The rich solvent, after removal of carbon dioxide, is

withdrawn from stripper 41 through pipe 46 and introduced into stripper 47 wherein acetylene is stripped out at a temperature of approximately 200 F. and at a reduced pressure of 2 p. s. i. a. Lean TDMAP is withdrawn from stripper 47 through pipe d and recycled to tower 35.

The acetylene withdrawn from the stripper 47 through pipe 50 is of high purity as indicated by the following approximate composition: 98.6 mol per cent acetylene, 0.8 mol per cent carbon dioxide, 0.5:mol per cent methyl acetylene and 0.06 mol per cent higher acetylenes. Acetylene of this purity meets the usual purity requirements for acetylene. However, the methyl acetylene content can be further reduced by a purification step involving scrubbing with naphtha. The methyl acetylene removal step is also shown on the attached drawing.

Reduction of the methyl acetylene content to less than 0.15 mol per cent is effected by passing the acetylene obtained from stripper 47 through pipe 54 into absorber 55. In absorber 55 the acetylene contacts light naphtha introduced through pipe 53 at atmospheric pressure, a temperature of to 60 F. and in a proportion of one gallon of naphtha for 2 to 3 cubic feet of acetylene. Methyl acetylene is removed from the high purity acetylene by this treatment. There is obtained from the upper portion of absorption tower 55 through pipe 56 acetylene which contains less than 0.15 mol percent methyl acetylene.

Since approximately of the acetylene stream is absorbed in the light naphtha in tower 55, it is necessary to strip acetylene therefrom. This is effected by passing the rich naphtha from absorber through pipe 60 into prestripper 61 wherein acetylene is stripped from the rich naphtha at a temperature of 160 to 210 F. and at a pressure of 2 p. s. i. a. The recovered acetylene is removed from prestripper 61 through pipe 62 and is usually recycled to absorber 55 through pipe 63.

After removal of acetylene, the naphtha is introduced into stripper 65 through pipe 64 wherein it is freed of methyl acetylene at atmospheric pressure and a temperature of 200 to 220 F. Methyl acetylene is taken ofi overhead from stripper 65 through pipe 66. Lean naph- Y. position of 98,9- mol per cent acetylene, 0.9 molper'cent carbon dioxide, 0.13 mol per cent methyl acetylene, 0.05 mol per cent vinyl acetylene and 0.015 mol per cent other acetylenes.

It is well to note. that when DMF is used inv place of TDMAP as the selective solvent for acetylene, the optional puriiication system comprising towers 55, 61 and 65 `for removing -small amounts of methyl acetylene from acetylene' becomes unnecessary. In, such event, part of the DME owing from tower 47 through line 48 tol tower 35 may be bypassed through an. additional` tower to strip methyl acetylene from the DMF stream; the DMF stream thusstripped of methyl acetylene would then be re-introduced at the toprnost plate in tower 47. Acetylene containing less than.0.15 mol per cent of methyl acetylene can be recoveredby such operation with DMF.

Obviously, many modications and variations of the invention,'as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

What is claimed is:

1. A process for recovering acetylene in pure form from a gas stream containing acetylene in low concentration and produced by the high-temperature decomposition or" a hydrocarbon, which comprises contacting said gas stream in a primary absorption zone at a pressure in the range of about atmospheric to 150 p. s.V i. g. with a highly parainic oil at a temperature between about 30 and F. and in a proportion just suicient to absorb substantially all aromatic hydrocarbons and only a minor portion of vinyl acetylene and diacetylene in said gas stream, thereafter subjecting said gas stream in a secondary absorption zone at a pressure in the range of about atmospheric to p. s. i. g. to further contact with a and 100 F. and in a proportion just suihcient to absorb vsubstantially all vinyl acetylene and diacetylene remaining in said gas stream, thereafter contacting said gas stream at a pressure in the range o f about atmosphericv to 150 p. s. i. g. with a selective solvent for acetylene at a temperature between about 30 and 100"A F., and recovering absorbed acetylene from said selective solvent. l

2. A process according to claim l wherein the proportion of parainic oil used in the primary absorption zone is approximately 1 gallon for every 30 to 60 cubic feet of gas contacting said oil.

3. A process according to claim 2 wherein the proportion of paranic oil used in the secondary absorption zone is approximately l gallon for every 3 to 6 cubic feet of gas contacting said oil.

4. A process according to claim 1 wherein the gas stream containing acetylene is produced by the partial combustion of a gaseous hydrocarbon with high-purity oxygen and said gas stream is washed with water prior to contact with the highly parainic oil in the first absorption zone.

5. A process according to claim l wherein the selectiv solvent is dimethyl formarnide.

6. A process according to claim l wherein the selective solvent is tris-dimethylamido phosphate.

7. A process according to claim 6 wherein the proportion of selective solvent contacting the gas stream is approximately l gallon for every 5 to l0 cubic feet of gas.

8. A process according to claim 7 wherein absorbed acetylene recovered from the selective solvent is scrubbed with naphtha to remove methyl acetylene therefrom.

9. in the process for recovering acetylene in pure form from a gaseous stream containing in low concentration acetylene, aromatic hydrocarbons, vinyl acetylene and diacetylene wherein said aromatic hydrocarbons,l vinyl acetylene and diacetylene are removed from said gaseous lstiearrt by absorption in a highly parainic oil prior toj the Aisolation of'said acetylene from said gaseous stream by Y absorption in a selective solvent for acetylene, the irn` Yprovernent which .comprises conducting the absolption `with said oil in' twosstages under vcontrolled conditions to remove from said gaseous stream at least 90% of said faromatic hydrocarbons without substantial absorption of said vinyl acetylene and diacetylenein the first stage and to remove from said gaseous stream substantially all of said vinylV acetylene and. diacetylene without substantial Y absorption of said acetylene in the second stage.

10. YThe process of claim 9 wherein the absorptionjis Vconducted in the rst and second stages at temperatures Vin the range of about V30 to 100 F. and at pressures in the range of about atmospheric pressure to 150 p. s.` i. g. 1l. The process of claim 9 ,wherein the proportion of highly parainic oil brought into contact with the gaseous streanrin the rrst 'absorption stage is oftthe order of i Mone-tenth of the proportion of said oil brought into con tact with said gaseous stream inthe second absorption s stage. 'Y

References Cited in the file of this patent UNITED STATS PATENTSy Baumann et al. Jan.;15, 1935 Scott `et a1. Feb, '77, 193,9 Isham et al May 16,1939V 'Murphree Dec. 12, 193,9 Hasche Apr. 15, 1941 Kosolapoff Apr. 4, 1950 Levine et al. Dec. 3,0, ,1952 

9. IN THE PROCESS FOR RECOVERING ACETYLENE IN PURE FORM FROM A GASEOUS STREAM CONTAINING IN LOW CONCENTRATION ACETYLENE, AROMATIC HYDROCARBONS, VINYL ACETYLENE AND DIACETYLENE WHEREIN SAID AROMATIC HYDROCARBONS,VINYL ACETYLENE AND DIACETYLENE ARE MOVED FROM SAID GASEOUS STREAM BY ABSORPTION IN A HIGHLY PARAFFINIC OIL PRIOR TO THE ISOLATION OF SAID ACETYLENE FROM SAID GASEOUS STREAM BY ABSORPTION IN A SELECTIVE SOLVENT FOR ACETYLENE, THE IMPROVEMENT WHICH COMPRISES CONDUCTING THE ABSORPTION WITH SAID OIL IN TWO STAGES UNDER CONTROLLED CONDITIONS TO REMOVE FROM SAID GASEOUS STREAM AT LEAST 90% OF SAID AROMATIC HYDROCARBONS WITHOUT SUBSTANTIAL ABSORPTION OF SAID VINYL ACETYLENE AND DIACETYLENE IN THE FIRST STAGE AND TO REMOVE FROM SAID GASEOUS STREAM SUBSTANTIALLY ALL OF SAID VINYL ACETYLENE AND DIACETYLENE WITHOUT SUBSTANTIAL ABSORPTION OF SAID ACETYLENE IN THE SECOND STAGE. 